The present invention generally relates to the stator bar end connections of a liquid-cooled generator. More particularly, this invention relates to a method of metallurgically joining copper conductors of a stator bar to a fluid coupling, whereby the joint is solidified in a manner that reduces the incidence of defect-induced corrosion.
Stator bars of a liquid-cooled electrical generator typically comprise a combination of solid and hollow copper strands, with opposing ends of the strands being brazed to a fluid coupling, referred to herein as a clip. The clip serves as both an electrical and fluidic connection for the stator bar. For purposes of the latter, the clip defines an interior chamber, referred to as a water box, into which the ends of the strands extend through an opening in the clip to permit flow of a liquid coolant, typically deionized water, between the clip and hollow strands. The coolant flows to or from the clip through a hose coupled to a hose connection of the clip. A braze metal metallurgically bonds the strands to each other and joins the clip to the peripherally outermost strands of the stator bar. Brazing is typically performed by placing a braze alloy, such as a preform formed of the alloy, between the strands and clip, and then heating the strands and clip with a torch or by induction heating to cause the braze alloy to melt and flow by capillary action. Once solidified, the braze alloy metallurgically bonds the strands to each other and to the fluid coupling so as to form a fluid-tight brazement between the stator bar and clip.
Over time, leaks may develop at the bar-clip connection as a result of the development of a leak path between strands and/or between strands and the clip. As reported in commonly-assigned U.S. Pat. Nos. 5,605,590 and 5,796,189, both to Manning et al., one leak mechanism that has been identified is attributed to corrosion of the braze alloy. Corrosion is believed to be initiated by stagnant water residing within concave pockets that are present in the surface of the brazement between the strands and clip. While Manning et al. disclose techniques by which the incidence of leakage can be reduced, there is an ongoing effort to further reduce the likelihood of leaks in view of the considerable downtime and cost involved in repairing such leaks.